The present invention relates to systems which use the earth as a heat exchange media and more particularly relates to a method and apparatus for forming a heat exchange system within the earth.
Most conventional, present day air conditioning systems used for heating and/or cooling buildings or like areas require relatively large amounts of energy (e.g. electricity and/or gas) to maintain the conditioned environment at a comfortable temperature. Recently, due to conservation efforts and increased energy costs, users have had to adjust their thermostats and operate their systems at less than desirable temperatures. This has resulted in a search for new developments and/or improvements in conventional air conditioning systems whereby the efficiency of a system can be increased at low initial capital costs but which will produce substantially lower operating costs in maintaining temperatures at more desirable levels throughout the year.
One promising approach for improving the efficiency of conventional air conditioning systems involves using the earth or ground, itself, as a heat exchange media for the fluids that are circulated through the air conditioner system. As known, the earth provides a very compact source or sink for heat. It has been calculated that a cylinder of earth 30 feet in diameter and 100 feet in depth can, by changing its temperature only 10.degree. F., source or sink up to 28 million Btu's of heat. This amount of heat exchange is enough for a five-month heating or cooling season wherein a heat pump system is operated 30 percent of the time at a rate of 30,000 Btu's per hour. Further, whereas ambient surface temperatures may vary as much as 80.degree. F. throughout the year, ground (earth) temperature at a depth of 6 feet varies only 20.degree. F. during the same period thereby maintaining a relatively constant temperature over long periods of time.
Several techniques have been proposed for accessing this heat exchange capability of the earth. One such technique involves installing a U shaped tubing in a substantially vertical wellbore that has been drilled into the earth. The well is filled with water to thermally couple the tubing to the earth surrounding the wellbore. Heat can then be exchanged between the earth and a fluid that is continuously circulated through the tubing. However, if the legs of the U-tubing are too close to each other, they, too, will be thermally coupled by the water in the well thereby seriously affecting the efficiency of the system. To overcome this problem, the wellbore, itself, has to have a large diameter and be very deep thereby making this heat exchange system relatively expensive to install.
Another known technique of accessing the heat exchange capacity of the earth involves installing a grid of pipes into trenches or ditches that are dug in the surface of the earth. The pipes are connected to form a continuous flowpath for a fluid which is to be heat exchanged with the earth. Unfortunately, the flowpath of this system can only substantially collect or reject heat in a flat plane downward into the earth thereby reducing its potential effectiveness by half. To increase the efficiency of such a system, the pipe grid would have to be buried substantially deeper in the earth or cover a large surface area, again substantially adding to the initial cost of installation of the system.
Therefore, it is believed that for the majority of present day air conditioner users to readily accept an earth heat exchange system as a means for increasing the efficiency of their air conditioning units and thereby reduce their operating costs, the initial cost for installing the earth heat exchange system must be considered relatively inexpensive when compared to the utlimate savings in the energy costs for operation.